On 02/19/2015 06:28 PM, Pantelis Antoniou wrote: > Hi Tony, > >> On Feb 19, 2015, at 20:16 , Tony Lindgren <tony@xxxxxxxxxxx> wrote: >> >> * Pantelis Antoniou <pantelis.antoniou@xxxxxxxxxxxx> [150218 07:03]: >>> Implement DT quirks for the am33xx beaglebone boards. >>> --- /dev/null >>> +++ b/arch/arm/mach-omap2/am33xx-dt-quirks.c >> ... >>> + >>> +/* >>> + * The board IDs for am33xx board are in an I2C EEPROM >>> + * We are very early in the boot process so we have to >>> + * read the EEPROM directly without using the I2C layer. >>> + * >>> + * Note that we rely on the bootloader setting up the muxes >>> + * (which is the case for u-boot). >>> + */ >>> + >>> +/* I2C Status Register (OMAP_I2C_STAT): */ >>> +#define OMAP_I2C_STAT_XDR (1 << 14) /* TX Buffer draining */ >>> +#define OMAP_I2C_STAT_RDR (1 << 13) /* RX Buffer draining */ >>> +#define OMAP_I2C_STAT_BB (1 << 12) /* Bus busy */ >>> +#define OMAP_I2C_STAT_ROVR (1 << 11) /* Receive overrun */ >>> +#define OMAP_I2C_STAT_XUDF (1 << 10) /* Transmit underflow */ >>> +#define OMAP_I2C_STAT_AAS (1 << 9) /* Address as slave */ >>> +#define OMAP_I2C_STAT_BF (1 << 8) /* Bus Free */ >>> +#define OMAP_I2C_STAT_XRDY (1 << 4) /* Transmit data ready */ >>> +#define OMAP_I2C_STAT_RRDY (1 << 3) /* Receive data ready */ >>> +#define OMAP_I2C_STAT_ARDY (1 << 2) /* Register access ready */ >>> +#define OMAP_I2C_STAT_NACK (1 << 1) /* No ack interrupt enable */ >>> +#define OMAP_I2C_STAT_AL (1 << 0) /* Arbitration lost int ena */ >> ... >> >> Uhh I don't like the idea of duplicating the i2c-omap.c driver under >> arch/arm.. And in general we should initialize things later rather >> than earlier. >> >> What's stopping doing these quirk checks later on time with just >> a regular device driver, something like drivers/misc/bbone-quirks.c? >> > > We have no choice; we are way early in the boot process, right after > the device tree unflattening step. Can you elaborate with an example of why not? Why can't the overlay happen at a later stage in the kernel boot as Tony suggests? One thought would be that ideally devices that are dependent on a particular board variant would be disabled in the base DT blob until you know what board you are. However, that assumes that they can be initialised at a later stage in the boot process and may be for some regulators or other devices this is not possible. I know you mentioned some time restrictions for some devices, but I still don't see why it could not happen later. Jon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
